Refractories



Patented Apr. 20, 1937 UNITED STATES PATENT OFFICE 2,077,795 nsrmcromssFrederic A. Harvey and Raymond E. Birch, Pittsburgh, Pa., assignors toHarbison-Walker Refraotories Company, Pittsburgh, Pa., 8. corporation ofPennsylvania,

' No Drawing.

Application June 13, 1935,

Serial No. 26,520 7 15 Claims.

" plated the use of rather pure magnesia-rich materials, for instanceburned magnesite consisting essentially of about 92 per cent of MgO, 2per cent of iron calculated as FeO, 1 per cent of SiOz,

and 5 per cent ignition loss, apparently on the theory that impurematerials would reduce the refractory value of the product.

We have found that certain'disadvantages attend the use of such highpurity magnesia-rich materials in the production of such refractories.One of the most serious of these is that the brick after firing possessquite unsatisfactory mechanical properties. For instance, as the brickcome from the kiln they are friable and their corners and edges areeasily scufied; because of this the brick must be handled quitecarefully and they are damaged easily in shipment. Moreover, the firingtemperatures necessary are generally so high as to be difiicult toobtain practically and commercially.

It is among the objects of this invention to provide refractories of theforegoing type in which the. aforementioned disadvantages are avoided orminimized, and which have improved strength characteristics.

The invention is predicated on our discovery that, contrary to whatwould have been expected, refractories made from forsterite materialsare substantially improved in character by using, instead of the highpurity magnesia-rich materials heretofore suggested, substances rich inmag-. nesia and of relatively high-lime content. The term- "high-limecontent as 'used herein has reference to magnesia-rich materials whichafter dissipation of volatile constituents, when present, throughcalcination contain in excess of about 3 per cent of lime (CaO). Thehigh-lime material is added in an amount such as to provide asubstantial lime content in the refractory. Some forsterite materials,such as olivine, contain small amounts of lime; we contemplaterefractories containing lime well in excess of that resulting from thatcontained in the olivine.

In the preferred practice of the invention there are usedlime-containing magnesites.- As illustrative of materials suitable forthe 'purposes of the invention, magnesites (dead-burned) of thefollowing compositions have been found to be satisfactory Maguesite PeruPercent MgO v 80.8 57.6 080 5. 8 25. 0 SiO; 6. 7 7. 8 R303 6. 5 9. 1Ignition loss- 0. 2 0. 5

. just indicated. For instance, there may be used high-lime brucites,electrically fused magnesia, and other magnesia-rich materials known tothose skilled in the art. While it is preferred to use magnesite indead-burned condition, this is not essential in all cases, for causticburned material may be used, although it is less suitable thandead-burned magnesite because it tends to undesirably increase thefiring shrinkage.

Materialscontaining less than about 3 per cent of lime are, in general,not suited for the purposes of the invention, and those containing morethan about 30 per cent of lime, i. e., materials of the dolomite class,tend'to introduce unfavorable factors. For most purposes, therefore, itis preferred to use magnesia-rich materials containing between about 3to about 30 per cent of lime.

, The base of the refractories provided by this invention is forsteritematerial, and we prefer to usenatural olivine minerals, which are richin forsterite, such as peridotite'or dunite. However, synthetic productsconsisting wholly or largely of magnesium orthosilicate may likewise beused. The minerals referred to are orthosilicates'of the magnesium-irontype containing,

preferably, not to exceed about 15 per cent of iron calculated as FeO,and with the iron advantageously less than about 10 per cent. An olivinetypical of those suitable for the practice of the invention containsabout 49 per cent of MgO, 7 per cent of FeO, 42 per cent of Si02, andminor amounts of customary impurities. In such an olivine the limecontent usually will not exceed a few tenths of 1 per cent.

The olivines may contain considerable amounts of alteration products inthe form of hydrous magnesium silicates, for example as talc andserpentine, and in some instances they may contain appreciable amountsof less refractory compounds such as pyroxenes. 'These nonforsteriticmaterials are converted by the added magnesia-rich material tocompounds'of high refractoriness, such as forsterlte and magnesiumferrite, thus conferring exceptionally high refractory value to thefinal product.

Thus the invention resides in the production of refractories fromforsterltematerials and magnesia-rich materials containing lime inamounts such that the latter have previously been considered notsuitable for making magnesium silicate refractories, to provideadvantages over similar refractories made from magnesia-rich materialsof greater purity and low in lime. In particular, the refractories madein accordance with this invention possess materially greater strengthand exceptional stability. In the practice of the invention olivineconstitutes the preferred base of the refractory, and therefore it maybe referred to hereinafter as exemplifying the practice of theinvention, but without limiting it thereto. Olivine, as notedhereinabove, treated in accordance with the invention, produces what isessentially a forsterite refractory, although, as will appear presently,other refractory materials may be present provided the olivine (orforsterlte material) constitutes the major portion of the refractorybatch.

In the practice of the invention there is added to a suitable olivine anamount of magnesia-rich, high-lime material sufficient to provide atleast about 0.8 per cent and not more than about 6 per cent of lime inthe product. Substantial benefits do not accrue, as we now believe,below about 0.8 per cent of lime, and above about 6 per cent -of limethe refractoriness may be reduced materially and excessive shrinkage athigh temperatures may be encountered. Between the limits stated we havefound that, more or less irrespective of the source of the magnesia-richmaterial, the strength of the fired product is in general proportionalto the lime content of the brick.

It is preferred in the manufacture of the reabove or below that to whichthe batch is submitted in service or in firing. Also, the olivine orother constituents of the batch may be pretreated by tabling, magneticor electrostatic separation, or by other purifying methods to improvetheir quality by removal of a part or all of objectionable impuritieswhich they may contain.

Advantageously high forming pressures are used.

Example 1.-As exemplifying the practice of the invention, reference maybe made to brick which were formed from a batch composed of 80 per centof olivine ground to pass 4 mesh, and 20 per cent of dead-burnedmagnesite, ground to pass mesh, of the composition,

identified as A in the foregoing table. The olivine was of the followinganalysis:

. Percent SiOz 40.9 MgO 48.9 FeO 7.7 A1203 0.7 CaO 0.2 CraOa 0.5Combined water 0.6

The batch containing about 1.4 per cent of CaO was tempered with waterand standard 9 714%; x2 inch brick were pressed from it in a hydraulicpress at a pressure of about 4000 pounds per square inch. The brick weredried for about 4 days at between 120 to 300 F. and then were burned toa temperature of about 2700 F. After firing these brick showed acold-crushing strength on flats of 3500 pounds per square inch. Incontrast, brick made from high purity magnesite in accordance with priorproposals tend to crumble easily after firing.

The exact manner of pressing the brick, and the type of press used, maybe adapted to the particular use to which the brick are to be put, aswill be understood. Also, the brick may be fired at higher or lowertemperatures, and the composition of the batch may be varied accordingto particular requirements as long as the brick contain a preponderantamount of forsterlte or forsterlte-forming material together withsuflicient of a magnesia-rich material of high-lime content to affordconversion 0 of the impurities to highly refractory forms, suitablebonding of the brick, and development of the desired properties, asindicated hereinabove.

The invention is not restricted to the manufacture of brick which arefired prior to being placed in service, but is applicable also" to themanufacture of brick and other shapes which are fired after being laidup in the furnace in which they are to be used. In such instances it isdesirable to add a temporary binder, of which a variety are availableand known in the art.

Example 2.--As exemplifying such practice of the invention, brick may bemade from a batch containing per cent of olivine of the compositiongiven in Example 1, 20 per cent of deadburned magnesite of thecomposition B in the foregoing table, these materials being ground as inthe preceding example, this batch containing about 5.2 per cent of CaOderived from the magnesite (5.0 per cent) and the olivine (0.2 percent). To this base mix there is added, as temporary binder, 4v per centof nitre-cake and 2 per cent of ground kaolin. The formed brick arecapable of being shipped without firing; after firthose skilled in theart. Other variations may be ing their cold crushing strength is about5000 pounds per square inch.

As illustrating the progressive increase. in strength with increase inlime content, withinthe limits stated, reference may be made to thefollowing table in'which there are presented the results-of tests whichwe have conducted:

" Olivine of composition in Example 1.

As noted above, artificially produced forsterite, or magnesiumorthosilicate, may alsobe used as the base of the refractories. Suchmaterial may be made from magnesia and silica in suitable proportions.Or, if desired for any reason, serpentine, talc, soapstone and the likehighly serpentinized and steatitized minerals may be used for the samepurpose by mixing them withsunlcient magnesia to bring their MgO contentto about 57 per cent, and heating to a suitable temperature, wherebythey are converted to forsteritewhich may then be treated with high-limemagnesia-rich material in accordance with this invention.

More suitably, however, serpentine hydrosilicate materials are treateddirectly in accordancewith the invention with high-lime magnesia-richmaterial as just described. As illustrative of this modificationreference is made to the following example.

Example 3.The refractories are made from a serpentine having thefollowing analysis:

Percent MgO -Q 37.4 SiOz 40.2 FeO+Fe2O3 6.4 A1203 1. 4 Ignition loss 14.2

The serpentine is calcined to 1450 C., or higher, to remove itsshrinkage, and it is then ground to pass a ll-mesh sieve. Magnesite ofComposition A of the foregoing table is then added in the ratio of 30parts thereof to '70 parts of the ground calcined serpentine, and themix is worked up and molded to form brick which are dried at about 250F. and then burned to approximately 2700 F.

If desired for any reason, the crude serpentine and magnesite are mixedbefore burning, one advantage being that this procedure avoidsprecalcination of the serpentine, although usually the pre-calcinationis desirable because the complete shrinking of the serpentine beforeadding the magnesia provides products of greater density than where thetwo materials are mixed before burning.

Althoughthe invention has been described with reference to themanufacture of shaped articles, such as brick, it is applicable equallyto the production of refractory compositions suitable for use as rammingmixes for forming portions of .furnace structures, as mortars, and thelike. For

and the like made without affecting the essence of the invention. Forinstance, small amounts of mineralizers, or catalysts, may be added tothe batch, among which are aluminum'phosphate or chloride, fluorides,nitrates, phosphates, borates, alkali metal silicates, and others withwhich the art is familiar. In general, these mineralizers will be usedin amounts from about 0.1. to about 5.0 per cent. Moreover, combinationsof magnesiarich materials high and low in lime may be usedprovidedsufficient lime is added, as stated hereinabove.

Also, there may be added-to the batch substantial amounts of otherrefractory materials, but in such instances the amount of such addedmaterial is to be suchthat the major portion (i. e., 50 per cent ormore) of the refractory consists of forsteritic material. As an exampleof such modified compositions, there maybe addedchromite between. about10 and 50 per cent of the batch, thus a typical composition wouldcontain about 50 per cent of olivine, 40 per cent of chrome ore, and 10per cent of a dead-burned magnesite, such as that identified as B in theforegoing table.

Other variations are also permissible. For instance, although it ispreferred in most instances to use the magnesia-rich material in finelydivided condition, yet where thereis used an olivine which isexceptionally low in hydrosilicates, and also low in magnesium silicatesmore siliceous than forsterite (e. g.,-pyroxenes) it is not so essentialthat the magnesia-rich mawhat we now consider to represent its bestembodiment. However, we desire to have it understood that, within thescope of the appended claims, the invention may be practiced otherwisethan as specifically described.

We claim:

1. That method of making forsterite refractory of improved characterwhich comprises the steps of grinding forsterite material to providecoarse granules, and mixing therewith magnesia-rich material containingfrom about 3 to about 30 per cent of lime in an amount sufficient toprovide at least about 0.8 per cent and not to exceed about 6 per centof lime.

2. That method of making forsterite refractory of improved characterwhich comprises the steps of grinding forsterite material to providecoarse granules, adding to a major quantity'of said forsterite materiala magnesia-rich material containing from about 3 to about 30 per cent oflime in an amount sufiicient to provide at least about 0.8. per cent andnot to exceed about 6 per cent of lime, shaping the batch thus produced,and burning the shaped article.

3. That method of making forsterite refractory of improved characterwhich comprises the steps of grinding forsterite material to providecoarse granules,- converting to finely divided form -a magnesia-richmaterial containing from about 3 to about 30 per cent of lime, andadding to said forsterite material an amount of said magnesiarichmaterial sufiicient to provide at least about 0.8 per cent and not toexceed about 6 per cent of lime.

4. That method of making forsterite refractory of improved characterwhich comprises the steps of grinding forsterite material to providecoarse granules, adding to a major quantity of said forsterite materialan amount of finely divided magnesia-rich material containing from about3 to about 30 per cent of lime, sufficient to provide at least about 0.8per cent and not to exceed about 6 per cent of lime, shaping the batchthus produced, and burning the shaped article.

.5. That method of making forsteriterefractory of improved characterwhich comprises the steps of grinding olivine material to provide coarsegranules, mixing therewith finely divided dead-bumed magnesitecontaining from about 3 to about 30 per cent oflime, to form a batchcontaining a major amount of olivine and from about 0.8 per cent toabout 6 per cent of lime, shaping the batch thus produced, and firingthe shaped article. 1 6. That method of making refractories of improvedcharacter from materials containing hydrated magnesium silicatecomprising the steps of grinding said silicate to provide relativelycoarse granules, adding thereto an amount of a magnesia-rich materialcontaining from about 3 to 30 per cent of lime and in;amount,sufilcientto convert said silicate to magnesium orthosilicate and suflicient toprovide at least about 0.8 per cent and not to exceed about 6 per centof lime, shaping the batch, and firing the shaped article.

7. A method according to claim 6, said silicate being calcined toeliminate shrinkage prior to 40 adding said magnesia-rich material.

8. That method of making forsterite refractory of improved characterwhich comprises the steps of grinding forsterite material to providecoarse granules, adding chrome ore in an amount 45 less than saidforsterite material, converting to finely divided form a magnesia-richmaterial containing from about 3 to about 30 per cent of lime, andadding to the batch an amount of said magnesia-rich material suflicientto provide at least about 0.8 per cent and not to exceed about 6 percent of lime.

9. A refractory of improved character comprising a major proportion offorsterite material and an. amount of magnesia-rich material containingfrom about 3 to 30 per cent of lime sufflcient to provide from about 0.8per cent to about 6 per cent of lime in the refractory.

10. An unburned refractory comprising more than about 50 per cent offorsterite material, and

an amount of magnesia-rich material containing from about 3 to 30 percent of lime sufiicient to provide between about 0.8 per cent and about6 per cent of lime in the refractory.

11. A burned refractory comprising a major proportion of magnesiumorthosilicate and about 0.8 per cent to about 6 percent of lime.

12. A burned refractory formed from a batch containing more than about50 per cent of olivine, -and magnesite high in lime to provide fromabout 0.8 per cent to about 6 per cent of lime.

13. A burned refractory comprising more than about 50 per cent ofmagnesium orthosilicate, from about 10 to about 50 per cent of chromeore, and about 0.8 per cent to about 6 per cent of lime.

14. A refractory composition of improved character comprising a majorproportion of olivine, chrome ore inan amount less than said olivine,and an amount of a magnesia-rich material containing between about 3 to30 per cent of lime suflicient to provide the refractory with not lessthan about 0.8 per cent and not to exceed about 6 per cent of lime.

15. A refractory composition of improved character comprising more thanabout 50 per cent of olivine, chrome ore more than 10 per cent and lessthan 50 per cent, and an amount of bumed magnesite containing betweenabout 3 to 30 per cent of lime suflicient to provide the refractory withfrom about 0.8 per cent to about 6 per cent of lime.

FREDERIC A. HARVEY. RAYMOND E. BIRCH.

